Isostatic presses with dry pressing chambers, particularly large such presses, are to advantage implemented in the form of a hollow cylindrical wall with one fixed and one removable end structure, the removable structure facilitating the insertion and withdrawal of a moulding tool. The inner jacket of the press wall is an elastomeric material behind which there is arranged a hydraulic chamber, which can be put under pressure. The moulding tool includes an elastomeric jacket which is contiguous to the press wall, or jacket in the press, and two end walls carried by end structures of the press.
When the hydraulic chamber of the press is put under pressure, forces are exerted which cause axial strain in the press. The moulding cavity of the tool will also be axially elongated and displaced in position relative a core possibly arranged therein. This results in that the powder mass being pressed experiences an axially uncontrolled movement relative the tool, whereby the pressed body can be damaged, be given an indeterminate axial length and be given a non-uniform inner structure. It should be particularly noted that plants of the mentioned type more accurately generate semi-isostatic pressure, since the pressing forces act in the normal plane to the axial direction of the pressing chamber and of the tool, the end walls thus providing reaction forces towards the powder shift developed in an axial direction. The axial strain of the press is therefore particularly unfavourable.
The problem is particularly pronounced when the tool includes a fixed member or core, which defines a moulding cavity together with the enveloping wall of the tool.